Dayton Audio DATS Dayton Audio Test System - Manual

DATS Loudspeaker Parameter Measurement Overview
and Impedance Accuracy Evaluation
by John L. Murphy, True Audio
Small-Signal Loudspeaker Parameters:
The so called “small-signal” parameters characterize the resonance of a speaker in normal operation.
Like many other electronic devices, loudspeakers have an input signal range where they work
normally. Above that range is some threshold above which the speaker exhibits misbehavior such as
increasing distortion, reduced output, or even catastrophic failure. The signal range where the speaker
operates normally is called the “linear region,” versus the “non-linear region” where distortion rises
rapidly. The small-signal region is that region between the noise floor and the point where the system
is no longer linear. This is the signal range where a loudspeaker’s small-signal parameters are
measured. Small-signal testing is usually performed at the lowest signal level where there is adequate
signal-to-noise ratio. See Figure 1 for a comparison of small-signal and large-signal ranges of
operation.
Figure 1: Small-signal versus large signal operating ranges
DATS calculates a loudspeaker transducer’s small-signal parameters from its impedance
measurement, using techniques established by Thiele
1
and Small
2
themselves. In addition to the
small-signal parameters DATS measures directly, it also calculates various other parameters.
The small-signal parameters of a loudspeaker are
1
:
f
S
The free air resonance
Q
ES
The electrical Q
Q
MS
The mechanical Q
Q
TS
The total Q
S
D
The piston area
V
AS
The equivalent volume of the suspension
R
E
The DC resistance of the voice coil